Merge pull request #11 from bjodah/generate-weights

Added new C++11 function: generate_weights

.gitignore

@@ -24,3 +24,4 @@ dist/
 doc/
 finitediff/_finitediff_templated.cpp
 *.egg-info
+tests/test_finitediff_templated

README.rst

@@ -44,6 +44,46 @@ Autogenerated API documentation for latest stable release is found here:
 (and development docs for the current master branch are found here:
 `<http://hera.physchem.kth.se/~finitediff/branches/master/html>`_).
 
+Examples
+--------
+Generating finite difference weights is simple using C++11:
+
+.. code:: C++
+
+  #include "finitediff_templated.hpp"
+  #include <vector>
+  #include <iostream>
+
+  int main(){
+    std::vector<double> x {-1, 0, 1};
+    auto coeffs = finitediff::generate_weights(0.0, x3, 2);
+    std::cout << "Zeroth order: " << coeffs[0] << " " << coeffs[1] << " " << coeffs[2] << std::endl;
+    std::cout << "First order: "  << coeffs[3] << " " << coeffs[4] << " " << coeffs[5] << std::endl;
+    std::cout << "Second order: " << coeffs[6] << " " << coeffs[7] << " " << coeffs[8] << std::endl;
+  }
+
+::
+
+   $ cd examples/
+   $ g++ -std=c++11 demo.cpp -I../include
+   $ ./a.out
+   Zeroth order: 0 1 -0
+   First order: -0.5 0 0.5
+   Second order: 1 -2 1
+
+and of course using the python bindings:
+
+.. code:: python
+
+   >>> from finitediff import get_weights
+   >>> import numpy as np
+   >>> c = get_weights(np.array([-1., 0, 1]), 0, maxorder=1)
+   >>> np.allclose(c[:, 1], [-.5, 0, .5])
+   True
+   
+
+see the ``examples/`` directory for more examples.
+
 Installation
 ------------
 Simplest way to install finitediff is to use the

examples/demo.cpp

@@ -0,0 +1,11 @@
+#include "finitediff_templated.hpp"
+#include <vector>
+#include <iostream>
+
+int main(){
+  std::vector<double> x {-1, 0, 1};
+  auto coeffs = finitediff::generate_weights(0.0, x, 2);
+  std::cout << "Zeroth order: " << coeffs[0] << " " << coeffs[1] << " " << coeffs[2] << std::endl;
+  std::cout << "First order: "  << coeffs[3] << " " << coeffs[4] << " " << coeffs[5] << std::endl;
+  std::cout << "Second order: " << coeffs[6] << " " << coeffs[7] << " " << coeffs[8] << std::endl;
+}

include/finitediff_templated.hpp

@@ -1,6 +1,11 @@
 #ifndef FINITEDIFF_TEMPLATED_HPP_IWIDN4CP6RGFHFVKSWG4HICEZE
 #define FINITEDIFF_TEMPLATED_HPP_IWIDN4CP6RGFHFVKSWG4HICEZE
 
+// Pre-processor macro __cplusplus == 201103L in ISO C++11 compliant compilers. (e.g. GCC >= 4.7.0)
+#if __cplusplus > 199711L
+#include <stdexcept>
+#endif
+
 namespace finitediff {
 
     template <typename Real_t>
@@ -19,10 +24,7 @@ namespace finitediff {
         // Generation of Finite Difference Formulas on Arbitrarily
         // Spaced Grids, Bengt Fornberg,
         // Mathematics of compuation, 51, 184, 1988, 699-706
-        //
-        // Notes
-        // -----
-        // If c is to be used repeatedly, consider transposing.
+
         Real_t c1, c2, c3, c4, c5;
         c1 = 1;
         c4 = x[0] - z;
@@ -71,6 +73,20 @@ namespace finitediff {
         }
         delete []c;
     }
+
+
+// Pre-processor macro __cplusplus == 201103L in ISO C++11 compliant compilers. (e.g. GCC >= 4.7.0)
+#if __cplusplus > 199711L
+    template<typename Real_t, template<typename, typename...> class Cont, typename... Args>
+    Cont<Real_t, Args...> generate_weights(const Real_t z, const Cont<Real_t, Args...>& x, const unsigned maxorder){
+        Cont<Real_t, Args...> coeffs(x.size()*(maxorder+1));
+        if (x.size() < maxorder + 1){
+            throw std::logic_error("size of x insufficient");
+        }
+        populate_weights<Real_t>(z, &x[0], x.size() - 1, maxorder, &coeffs[0]);
+        return coeffs;
+    }
+#endif
 }
 
 

scripts/ci.sh

@@ -1,4 +1,5 @@
 #!/bin/bash -xeu
+(cd tests/; make)
 PKG_NAME=${1:-${CI_REPO##*/}}
 if [[ "$CI_BRANCH" =~ ^v[0-9]+.[0-9]?* ]]; then
     eval export ${PKG_NAME^^}_RELEASE_VERSION=\$CI_BRANCH

tests/Makefile

@@ -0,0 +1,11 @@
+CXX ?= g++
+CXXFLAGS ?= -std=c++11 -Wall -Wextra -Werror -Wpadded -pedantic -I../include -fno-omit-frame-pointer
+
+.PHONY: test debug clean
+
+test: test_finitediff_templated
+	./test_finitediff_templated
+
+test_finitediff_templated: test_finitediff_templated.cpp ../include/finitediff_templated.hpp
+	$(CXX) $(CXXFLAGS) -o $@ $<
+